There is evidence for activation of hemostasis by endotoxin via cytokine induction, and vascular relaxation via increased nitric oxide synthesis. This proposal intends to study the effects of low-dose intravenous endotoxin infusion on hemostasis and cerebral vasomotor reactivity on 20 subjects over the next year, some healthy volunteers, and some with stroke risk factors. They will be admitted for 30 hours for i.v. endotoxin infusion, and sequential assays for hemostatic markers and repeated cerebral vasomotor reactivity tests.